Stuart will correct me if I am wrong .
I think Historic Mortars could fire anything that fitted in them .ie;- Rocks ,Solid Iron Balls and various explosive or incendiary Balls depending if anti personel, with fragmenting cases and loose shrapnel mixed in the charge, to full explosive filled destruction balls against buildings ,ships etc.
Modern Artillery Mortars can fire high-explosive rounds, smoke rounds, illumination rounds, and anti-personnel rounds. Depending on the situation .